A mobile communication system supporting LTE (Long Term Evolution)-Advanced can perform CA (Carrier Aggregation) using a Pcell (Primary Cell) that is a serving cell in a PCC (Primary Component Carrier) and an Scell (Secondary Cell) that is a serving cell in an SCC (Secondary Component Carrier).
Moreover, radio characteristics (delay characteristic and attenuation characteristic) differ among cells. For this reason, when “Inter-band CA” is performed in the mobile communication system supporting LTE-Advanced, TA (Timing Alignment) control suitable for each of cells having different radio characteristics needs to be performed.
Specifically, in LTE-Advanced, in the case of performing “Inter-band CA”, a Pcell and Scells are grouped into TAGs (Timing Advance Groups) each having equivalent radio characteristics as illustrated in FIG. 4, and TA control is performed in each of the TAGs.
Such TA control is called as “Multiple Timing Advances (MTA) control”. Note that the above groups include two types, that is, a pTAG (primary TAG) that includes a Pcell, and an sTAG (secondary TAG) that only includes Scells.
In the meeting for developing standardization of LTE, agreements as illustrated in FIG. 5 was made for “Pathloss reference cells” and “timing reference cells” in the TAGs.
Here, the “timing reference cell” is a “DL Cell” to which is referred in order to adjust timing in a downlink or a clock in a mobile station UE. The “DL Cell” here indicates a downlink cell where to perform a downlink communication.
Moreover, the “Pathloss reference cell” is a “DL Cell” to which is referred in order to estimate a path loss in the downlink.
Specifically, for a Pcell in the pTAG, it is defined that the “timing reference cell” and the “Pathloss reference cell” are the Pcell, as illustrated in FIG. 5 and FIG. 6.
Moreover, it is defined that the “timing reference cell” for an Scell in the pTAG is the Pcell.
Moreover, it is defined that the “Pathloss reference cell” for an Scell in the pTAG is the Pcell, or one of “SIB2 linked cells” of the Scell designated by a network.
Here, the “SIB2 linked cell” of the Scell is a “UL Cell” linked with the Scell by an SIB2. Here, the “UL Cell” indicates an uplink cell where to perform an upstream communication.
Moreover, it is defined that the “timing reference cell” for the Scell in an sTAG is one of cells in the sTAG selected by the mobile station UE, as illustrated in FIG. 5 and FIG. 7.
Here, the network is unable to designate the “timing reference cell” for the Scell in the sTAG.
In addition, the “Pathloss reference cell” for the Scell in the sTAG is one of “SIB2 linked cells” in the Scell selected by the mobile station UE.
Here, the network is unable to designate the “Pathloss reference cell” for the Scell in the sTAG.